Hitherto, a typical air conditioning system is known in which a heat source unit, such as a heat pump, generates cold/hot water and in which a water pump conveys the cold/hot water to perform cooling/heating of an indoor space. The air conditioning system of this method typically adopts a method in which water is sent at a constant water temperature irrespective of the load, by, for example, supplying cold water of 16 degrees C. to the indoor unit during cooling and supplying hot water of 35 degrees C. to the indoor unit during heating. With this method, in a period in-between seasons or in a case in which the load is small, intermittent operation, such as stopping the heat source unit or stopping the supply of water to the indoor unit with a three-way valve, is carried out when a room temperature reaches a preset value. Accordingly, comfort is compromised and operating efficiency is reduced.
Furthermore, some air conditioning systems include a function that allows a business person in charge of installation to set a target water temperature in accordance with the outside air temperature. No problem will occur if the water temperature and the load match each other; however, under some conditions, an operation with insufficient power may be carried out in which the water temperature is low with respect to the load, or an operation with excessive power may be carried out in which the water temperature is high with respect to the load. Accordingly, a decrease in comfort and operating efficiency is, likewise, brought about.
As a measure to overcome these problems, Patent Literature 1 discloses a control method in which a target temperature of the water supplied by the heat source unit is reset on the basis of a variation between a target indoor temperature that has been set by a user and the current indoor temperature and in which a target water flow rate is reset on the basis of a variation between the reset target water temperature and the current target water temperature. Specifically, the air conditioning system of Patent Literature 1 is provided with a refrigerant circuit including a compressor, a decompression device, and a heat exchanger and with a cold/hot water circulating circuit that is capable of exchanging heat with the refrigerant circuit. The cold/hot water circulating circuit supplies cold/hot water to the indoor units. This air conditioning system sets a new target water temperature from a variation between the current indoor temperature and the target indoor temperature and changes the power of the heat source unit, that is, the frequency of the compressor, so that the water temperature reaches a target value.